Glaucoma is attributable basically to a sustained or repeated increase in the intraocular pressure and causes functional and further organic disorders to the eye. For the treatment of this disease, it is considered to be a matter of urgency to reduce the increased intraocular pressure to the normal level to maintain the proper visual function (Masakichi Mikuni and Kazuo Iwata, "Glaucoma," Kanehara Shuppan Co., Ltd., 1968).